LONDON — Two of the world’s leading chemical manufacturers, the Huntsman Corporation and Clariant of Switzerland, terminated a planned multibillion-dollar merger on Friday, bowing to pressure from activist investors who opposed the deal.

The deal’s demise was the latest success for activist shareholders, who have put some of the world’s largest companies in their sights and are exerting greater influence over corporate strategy.

The proposed all-stock transaction, called a “merger of equals” by Clariant and Huntsman in May, would have been the latest consolidation in the chemicals industry and created a business with a combined market value of about $15 billion.

Some of the industry’s biggest names have sought mergers to gain scale and cut costs, including recent deals between Dow Chemical and DuPont and between Bayer and Monsanto.

“Given the continued accumulation of shares by activist investor White Tale Holdings and their opposition to the transaction, now supported by some other shareholders, we believe that there is simply too much uncertainty as to whether Clariant will be able to secure the two-thirds shareholder approval that is required to approve the transaction under Swiss law,” Peter R. Huntsman, the Huntsman chief executive, and Hariolf Kottmann, the Clariant chief executive, said in a news release.

On Friday, Huntsman and Clariant said they remained convinced that the proposed deal was “in the long-term best interests of all of our shareholders” but opted to avoid the continued costs and disruption in trying to push the deal forward.

Neither company will pay a breakup fee.

Clariant said on Friday that White Tale, an investment vehicle formed by the hedge fund manager Keith Meister and the investment fund 40 North, had accumulated more than 20 percent of the Swiss company’s shares.

The deal had been forecast to save about $400 million a year. The combined company would have manufactured coatings, resins and other industrial chemicals and employed more than 32,000 people worldwide.

Huntsman was founded in 1970 by Jon M. Huntsman Sr., a former Nixon administration official who founded the company and soon began making containers for McDonald’s Big Macs. One of his sons is Peter R. Huntsman, the company’s current chief executive.

Another son, Jon M. Huntsman Jr., is a former Utah governor, ambassador to China and Republican presidential candidate who recently was confirmed as the United States ambassador to Russia.

Clariant was created in 1995 when it was spun off from the chemical company Sandoz.

The collapse of the Huntsman-Clariant deal is the latest sign of the increasing power of activist investors.

Avon Products, the door-to-door seller of beauty products, said in August that its chief executive, Sherilyn S. McCoy, would step down next year. Activist investors have pressed the company to reshape its management and act faster to reverse its declining fortunes.

Mr. Peltz and his investment firm, Trian Partners, have recently turned their focus to the consumer-products giant Procter & Gamble, which previously faced pressure from another billionaire investor, William A. Ackman.